1. Field of the Invention
This invention relates to devices and methods for the phototherapeutic treatment of illness and diseases.
2. General Background
Phototherapy is a promising clinical tool for the treatment for many conditions, including seasonal affective disorder, bulimia nervosa, herpes, psoriasis, sleep disorders, acne, and skin cancer.
Phototherapy is especially promising as a treatment for hyperbilirubinemia, a common condition affecting 60–70% of all full-term infants. Hyperbilirubinemia is caused by the accumulation of excess bilirubin in the blood and skin of the infant. This excess bilirubin turns the skin and sclera a characteristic yellow color. If left untreated, extreme cases of hyperbilirubinemia can result in neurological insult (kernicterus) or even death. A common treatment for hyperbilirubinemia is phototherapy, in which the infant is exposed to light in a range corresponding to the peak absorption spectra for bilirubin (blue-green, 400–520 nm). This light changes the form of the bilirubin to a different isomer that is more readily eliminated by the body. The effectiveness of phototherapy depends on several factors: the spectrum of light delivered, the amount of surface area exposed to the light, the duration of the treatment, and the intensity of the light.
A number of different light sources can be used for phototherapy. Traditionally, broadband sources have been used, such as fluorescent, halogen, or incandescent light. However, it has been recently been suggested that light emitting diodes (LEDs) can be an effective phototherapeutic light source.
In the past, phototherapeutic light sources have been arranged into uniform arrays, typically in a rectangular pattern. Such a configuration can produce an acceptable average light intensity for phototherapy treatment. For instance, it has been found that a 10 inch by 20 inch array of approximately 750 blue LEDs suspended 12 inches above a subject can produce sufficient intensity, approximately 35 microwatts/cm2, in the spectrum of interest (400 nm to 520 nm), to be a clinically useful phototherapy device for the treatment of hyperbilirubinemia. However, there are a number of drawbacks to using such a simple rectangular array.
First, the distribution of light from a simple rectangular array will not be uniform. The intensity will be significantly higher underneath the center of the array than around the periphery. Thus, parts of the subject's skin will receive sufficient light intensity, but other parts will not, thereby limiting the effectiveness of the phototherapy.
Additionally, if the subject is not placed directly under the center of the array, he or she will not receive the full benefit of the delivered light energy. To address these concerns as they apply to phototherapy for jaundiced infants, the IEC (International Electronics Commission) has developed a standard that describes a method to measure the uniformity of phototherapeutic light. This standard also recommends that the ratio between lowest and highest intensity portions of the light delivered to the infant be greater than 0.4. See IEC 60601-2-50 (2000): “Medical Electrical Equipment—Part 2–50: Particular Requirements for the Safety of Infant Phototherapy Equipment.”